Remove sublayer transform from the Weblayer API

It's dead code. Let's ditch it.

R=jamesr@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/169183002

git-svn-id: svn://svn.chromium.org/blink/trunk@167258 bbb929c8-8fbe-4397-9dbb-9b2b20218538